Engine noise barrier

ABSTRACT

A co-injection molded air intake manifold shell comprises an inner and outer skin layer separated by a sound absorbing or sound insulation core. Each skin layer is composed of a polyamide resin which, optionally, contains glass fiber reinforcement and high specific gravity fillers such as barium sulfate or tungsten. The sound insulating core is composed of a high density material having a foam structure, such as a polyamide resin. Skin layers are provided with a plurality of pockets to permit distribution of localized lumped masses at predetermined locations tailored to increase noise transmission losses. A single layer air intake manifold shell having non-uniform thickness is also provided. The thickness of the single layer air intake manifold shell is larger over preselected noise sources of larger amplitude to maximize noise attenuation for a nominal air intake manifold shell thickness.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to sound attenuation systems thatrestrict airborne and structural-borne sound wave transmission; and moreparticularly, to an air intake manifold shell having a combination ofcompositional and structural features that significantly reduce engineinduced noise.

[0003] 2. Description of the Prior Art

[0004] Continued efforts to reduce vehicle weight and cost have ledautomobile manufactures to replace metal components with alternativematerials. Plastic air intake manifolds represent one example of thistrend. These air intake manifolds cost and weigh less thus reducingmanufacturing costs while increasing fuel efficiency. Air intakemanifolds currently sold to original equipment manufacturers aresegregated into several feature categories. Significant featurecategories typically considered include cost, temperature performance,aesthetics, recycling aspects and noise abatement performance.

[0005] While materials such as nylons have been used in air intakemanifold applications, such attempts to meet automotive needs haveencountered manufacturing and performance issues; there remainssignificant room for improvement in low cost noise abatement air intakemanifolds. Because of the imminent noise radiation increase with plasticcomponents, most engine systems require air intake manifolds or shieldsas a separate component. Typical materials used for acoustic shields arepolyurethanes, foam and fiber pads, usually treated onto the plasticshell. These all require post injection molding operations and aretherefore costly. In addition, the noise attenuation provided by suchshields has been unsatisfactory.

[0006] Conventionally, noise has been reduced using air intake manifoldsof the type described by increasing the surface density of the airintake manifold shell. In cases where a noise source is identified,stiffening ribs have been added, or the mass of the air intake manifoldshell has been increased.

[0007] No one has taken the approach of incorporating the noiseshielding function into the plastic component itself, such as utilizingco-injection technology, and vibration welding to improve noiseabatement performance at a lower cost. Nor have superior soundtransmission loss materials been used in air intake manifold shellfabrication.

[0008] Accordingly, there remains a need in the art for an air intakemanifold having a compact, light-weight construction, improved noiseabsorption and attenuation characteristics, which operate collectivelyto reduce engine noise economically, in a highly reliable manner.

SUMMARY OF THE INVENTION

[0009] The present invention provides an improved air intake manifoldshell that provides significantly improved noise reduction at low cost.Materials having superior sound transmission loss properties arecombined with a barrier construction especially suited to provideincreased absorption, and superior sound transmission loss properties.

[0010] In one embodiment, the invention provides a co-injection moldedair intake manifold shell comprising an inner and outer layer separatedby a sound-absorbing core. Each of the outer layers is composed of apolyamide resin. Preferably, the polyamide resin contains glass-fiberreinforcement and mineral filler such as barium sulfate. The inner layeris composed of a low-density, high damping material having a foamstructure, and or dispersed high-density material such as a glass-fiberreinforced and mineral filled polyamide resin.

[0011] Optionally, the layers are provided with a plurality of blistersto distribute localized increased core thickness (pockets) atpredetermined locations across the air intake manifold shell surface,the locations being selected to increase noise transmission losses. Thenoise transmission loss is further improved by introducing higherdensity materials into the localized pockets.

[0012] In an alternative embodiment, a double layer air intake manifoldshell comprises an inner and outer layer separated by an air core.

[0013] In yet another embodiment, a single layer air intake manifoldshell is comprised of a polyamide resin containing glass and mineralfillers such as barium sulfate or high damping carbon nano-tubes.Optionally, the single layer air intake manifold shell has non-uniformthickness. The thickness is preferably greatest over preselected areasfrom which emanate noise transmissions having larger amplitude, toincrease noise transmission losses.

[0014] The present invention incorporates barrier and absorptiontechnologies in plastic constructions thereby reducing overall noisetransmittance while at the same time reducing space, weight and costrequirements of existing technologies.

BRIEF DESCRIPTION OF DRAWINGS

[0015] The invention will be more fully understood and furtheradvantages will become apparent when reference is had to the followingdetailed description and the accompanying drawings, in which:

[0016]FIG. 1 is a perspective view illustrating a typical air intakemanifold shell construction;

[0017]FIG. 2 is a cross sectional view depicting a co-injected airintake manifold shell;

[0018]FIG. 3 is a cross sectional view of a co-injected air intakemanifold shell provided with a blister; and

[0019]FIG. 4. is a cross sectional view depicting a two-layer air intakemanifold shell having an air core.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Sound attenuating thermoplastic materials designed for use asbarrier systems in the automotive and consumer industries have certainacoustical characteristics that vary as functions of the stiffiess anddensity of the barrier material. An important acoustic property for abarrier material is its sound transmission loss (STL). The STLdetermines the effectiveness of the material in attenuating unwantednoises. Accordingly, a barrier is a material that causes the sound waveto lose energy as the wave is transmitted through it. The soundtransmission loss is the proportion of energy lost as a result of soundbeing transmitted through the material. In general, a higher STL meansthe barrier exhibits better noise attenuation performance.

[0021] While not being bound by any specific theory, the transmissionloss coefficient is defined as: $\begin{matrix}{\tau = \left( \frac{P_{t}}{P_{i}} \right)^{2}} & (1)\end{matrix}$

[0022] Where:

[0023] P_(t)=Transmitted sound power

[0024] P_(i)=Incident sound power

[0025] And the sound transmission loss in a specified frequency band isten times the common logarithm of the ratio of the airborne incidentsound power to the transmitted sound power, expressed in decibels:

STL=10log1/π  (2)

[0026] Conventional methods for reducing noise, as applied to a platefor example, comprise either increasing the surface density of the plateor, for cases wherein the noise source is identified, adding stiffeningribs or mass uniformly over substantially the entire surface area of theplate. In order to raise the sound transmission loss capability of asingle panel or barrier made from such material and used as a partitionbarrier, its surface mass must be increased.

[0027] This is achieved according to the empirical mass-law equation:

STL=20log ₁₀ρ_(s)+20log f−C

[0028] ρ_(s)=surface density of barrier in kg/m²

[0029] Where:

[0030] f=frequency in Hz

[0031] C=constant (in above units 47.2)

[0032] STL=Sound transmission Loss in dB

[0033] A typical single panel STL curve defines various frequency rangesand their effects on transmission loss. The STL performance can begrouped into three controlling regions. These are:

[0034] 1. Stiffness and resonance controlled region—less than 200 Hz;

[0035] 2. Mass controlled region (Mass Law)—between 200 and the criticalfrequency, which ranges from about 5000 Hz to 20,000 Hz, depending onthe parameters set forth in equation 4 hereinafter;

[0036] 3. Wave coincidence (at the critical frequency) and stiffnesscontrolled region—above the critical frequency.

[0037] The increase in surface mass tends to shift the criticalfrequency down. At this frequency, the incident sound wave couples withthe bending wave in the panel, thus increasing the motion of thebarrier, which is then transmitted, to the other side. This phenomenoncauses a decrease in the sound transmission loss and hence is the dip inthe STL curve as shown above. Having a lower critical frequency reducesthe effective range of application of the material.

[0038] The critical frequency of a homogenous barrier is given by:$\begin{matrix}{f_{c} = {{\frac{c^{2}}{2\pi}\sqrt{\frac{\rho \quad s}{B}}} = {\frac{c^{2}}{1.8t}\left( \frac{\rho \quad m}{E} \right)}}} & (4)\end{matrix}$

[0039] please change the subscripts to match later text

[0040] Where:

[0041] c=Speed of sound in the propagating medium, m/sec

[0042] ρ_(s)=Surface density of the barrier, Kg/m²

[0043] B=Bending stiffness of the barrier per unit width N−m=Et³/12

[0044] E=Youngs Modulus of the barrier, N/m²

[0045] ρ_(m)=Volume density of the barrier, Kg/m³

[0046] One way to improve the STL performance significantly withoutnecessarily increasing the “mass” is to have a double wall barrierconstruction. Recent developments in the Noise, Vibration and Harshness(NVH) technology field, indicate that double layer systems separated byair gaps offer exceptionally high noise barrier characteristics comparedto a single panel.

[0047] The present invention provides an air intake manifold shellhaving superior noise abatement properties. It has been discovered thatthese superior noise abatement properties are afforded by air intakemanifold shell constructions, which comprise:

[0048] a) a single layer of uniform thickness with optimized density andmass/thickness distribution;

[0049] b) a double layer separated by a sound absorbing core(sandwiched) layer;

[0050] c) a single or sandwich structure with optimally distributedlumped masses “local bumps” or “pocket blisters;” and

[0051] d) a single layer structure with optimally distributed ribstructures

[0052] Engine air intake manifold shell structures a) and b) affordnoise reduction according to the “mass law” theory, and the “doublelayer” theory, respectively. Core layers in case b) are air pockets,foam structure, high damping elastomer, and/or high-density materials.The core material that can be an absorption type material acts as adecoupler, since it decouples or isolates the two barrier walls fromeach other, and thereby aids in enhancing the STL performance. Case c)reduces noise by shifting the local natural frequencies away from theinput driving frequency domain; lowering the frequency by adding lumpedmass. Case d) reduces noise by shifting the frequency through stiffeningthe local area. The location and the number of the distributed massesand pockets can be optimized based on the nature of noise to filter out.

[0053] Use of a single layer structure having optimally distributed ribstructures reduces noise by shifting the local natural frequencies awayfrom preselected frequency components that are identified as undesirablesounds, such as rumbling, hissing and air rush noise. They lower thefrequency by adding local ribs; increase the frequency by stiffening thelocal area.

[0054] The sound transmission loss (STL) behavior was tested on extrudedsheets of Capron® 8233 nylon 6 from Honeywell sandwiched with a 6-mm airgap. Structures having this construction exhibited a substantialincrease in sound barrier attenuation properties. The high performanceof a double wall system takes place only after the system experiencesdouble wall resonance. This phenomenon takes place due to themass-air-mass resonance of the double wall, produced when the panels actas two masses connected by a spring or spacer. Double wall resonancefrequency is given by: $\begin{matrix}{{f_{dw} = {\frac{k_{3}}{\sqrt{wd}}\quad {Hz}}}{{Where}:\begin{matrix}{w = \quad {{Equivalent}\quad {surface}\quad {density}}} \\{= \quad {w_{1}{w_{2}/\left( {w_{1} + w_{2}} \right)}}} \\{{w_{1}w_{2}} = \quad {{Surface}\quad {density}\quad {of}\quad {individual}\quad {barrier}\quad {walls}}} \\{d = \quad {{Thickness}{\quad \quad}{of}\quad {the}\quad {spacer}\quad {material}\quad {between}\quad {the}}} \\{\quad {{two}\quad {barriers}\quad \left( {{assumption}\quad \text{:}\quad {the}\quad {weight}\quad {of}\quad {the}} \right.}} \\\left. \quad {{spacer}\quad {material}{\quad \quad}{is}\quad {negligible}} \right) \\{k_{3} = \quad {Constant}} \\{{= \quad 42},{{if}\quad w\quad {is}\quad {in}\quad {Kg}\text{/}{{sq}.m}},{{and}\quad d\quad {is}\quad {in}\quad m}} \\{{= \quad 120},{{if}\quad w\quad {is}\quad {in}\quad {lb}\text{/}{{sq}.{ft}.}},{{and}\quad d\quad {is}\quad {in}\quad {inch}}}\end{matrix}}} & (5)\end{matrix}$

[0055] At frequencies lower than the f_(dw), the double wall systembehaves like a single wall having a mass equivalent to the sum of themasses of the two barriers. Therefore, in this region, the performanceof the double wall and single wall systems is the same, provided themass is the same. However, right at that frequency, sound transmissionloss is decreased below that of a single barrier. For frequencies abovethe f_(dw), the two walls decouple from each other, and the soundtransmission loss increases significantly (18 dB/Octave theoretically)until it is limited by the critical frequency of either of the twopanels. Thus, the double wall resonant frequency in the low frequencyregion, and the critical frequency of the individual walls at the highfrequency limit the effectiveness of the double wall system.

[0056] At the f_(dw) and cavity resonance (which is due to the physicalsize and shape of the air gap or cavity separating the two layers), acore layer with sound absorption properties can serve as a couplingmaterial. This coupling material can significantly increase soundtransmission loss, and introduce a damping effect to the mass-air-mass(f_(dw)) and cavity resonances. The sound absorbing property of thecoupling material causes the sound wave amplitude to decay withdistance. A general solution for the ratio of transmitted to incidentsound pressure is then: (according to F. J. Fahy, Sound and StructuralVibration: Radiation, Transmission and Response—Academic, New York,1987). $\begin{matrix}{\frac{{\overset{\sim}{P}}_{t}}{{\overset{\sim}{P}}_{i}} = {- \frac{4j\quad \omega^{3}\rho_{0}^{2}c\quad {\gamma \left( {\sinh \quad \gamma \quad d} \right)}^{- 1}}{{\gamma^{2}{\overset{\sim}{a}}_{1}{\overset{\sim}{a}}_{2}} - {\omega \quad \rho_{0}{y\left( {{\overset{\sim}{a}}_{1} + {\overset{\sim}{a}}_{2}} \right)}\coth \quad \gamma \quad d} + {\omega_{0}^{2}\rho_{0}^{2}}}}} & (6)\end{matrix}$

[0057] Where:

[0058] ã₂=jω({tilde over (z)}₁+ρ₀c)

[0059] ã₂=jω({tilde over (z)}₂+ρ₀c)

[0060] {tilde over (z)}₁=m₁(jω+η₁ω₁)−js₁/ω

[0061] {tilde over (z)}₂=m₂(jω+η₂ω₂)−js₂/ω

[0062] γ=propagation constant of coupler

[0063] η_(1,2)=mechanical loss factors of the barrier

[0064] For large attenuation constants of the coupling material, thelayers become decoupled. The low frequency mass-air-mass resonancebecomes less pronounced. Similarly the sound absorption of the couplersuppresses cavity resonance. According to Fahy, the maximum pressuretransmission ratio is: $\begin{matrix}{\frac{{\overset{\sim}{P}}_{t}}{{\overset{\sim}{P}}_{i}} = {{- {j\left( \frac{2\rho_{0}c}{\omega \quad m_{1}} \right)}}\left( \frac{2\rho_{0}c}{\omega \quad m_{2}} \right)\left( \frac{K}{\beta} \right){\exp \left( {{- \alpha}\quad d} \right)}}} & (7)\end{matrix}$

[0065] Which gives $\begin{matrix}{{STL} = {{{TL}\left( {o_{1}m_{1}} \right)} + {{TL}\left( {o_{1}m_{2}} \right)} + {8.6\alpha \quad d} + {20\quad {\log_{10}\left( \frac{\beta}{K} \right)}}}} & (7)\end{matrix}$

[0066] The component 8.6αd (dB/m) corresponds to the transmission lossof the sound absorbing coupler.

[0067] As previously noted, one of the options for improving theperformance of a barrier material is to increase the “mass” (or surfacedensity) of the barrier. As has been demonstrated by previous studies,doubling the surface density of a barrier improves the STL performanceby 6 dB. Further, doubling the surface density again improves the STLperformance by 12 dB. This approach, may not be practical frommanufacturing consideration as a significant weight and cost increaseoccurs. In addition to the increase in mass, the critical frequency ofthe material is lowered, which is not desirable. To establish abaseline, a program was written in Matlab release 11 to calculatetheoretically and plot the STL curve based on varying thickness andproperty parameters. Next, newly developed grades of Nylon 6, havingadded thereto different levels of barium sulfate filler, were selectedto calculate and plot the NVH performance at the single and double themass configurations and against aluminum.

[0068] Capron® 8267 nylon 6 (15% glass fiber and 25% mineral) andCapron® 8233 nylon 6 (33% glass fiber) from Honeywell were selected, andcompared against each other and aluminum in order to understand thespecific gravity and density effects on the performance. The resultsshowed that the performance of the two materials was equivalent (not asignificant change in the specific gravity), but below that of aluminumdue to the density effects.

[0069] The results show a significant improvement in the STL performancedue to the composition of the new material. The STL were calculated for24″×24″ sheets using SAE J1400 formulae. The SAE J1400 basedcalculations were found to substantially agree with the theoreticalfield incidence calculated curve. For correlation purposes, the fieldincidence theoretical calculated TL's are interspersed with theexperimental results.

[0070] STL tests were conducted on 3 mm thick panels. The samples testedare distributed according to the following: Measured data Sample Surf.Wt.: No. SAMPLE DESCRIPTION Kg/m² (lb/ft²) 1 XA2934 nylon 6 basedpolymer: 6.0 (1.2) Single Wall 2 XA2935 nylon 6 based polymer: 6.3 (1.3)Single Wall 3 8233G HS BK 102 nylon 6 based polymer: 4.0 (0.8) SingleWall 4 8233G HS BK 102 nylon 6 based polymer: 8.0 (1.6) Double Wall (2layers separated by 6 mm air gap)

[0071] A thin lead panel of 4.9 Kg/m² (1.0 lb/ft²) surface weight wasused to compute the correlation factor as referenced in SAE J1400. Thelowest usable frequency band of measurement for this test (in a 508 mmby 508 mm, or 20 inch by 20 inch opening) is 125 Hz (based on the 0.72 mor 2.36 ft) diagonal of the opening between the source room and thereceiving room.

[0072] Measurements were made at six microphone locations in the sourceroom and at one location 100 mm (4 inches) away from the sample, sixtimes in the receiving room.

[0073] STL data obtained from the samples clearly show the increase inperformance obtained using the new material over the existing Capron®8233 resin material, for example. STL data was obtained for a singlesheet of Capron® 8233 resin vs. the double wall design. The resultsclearly show the superior performance of the double wall system over thesingle wall structure. The critical frequency dips in the lowerfrequency region of the double wall system can be eliminated using anabsorbing core layer. The high specific gravity of Capron® XA2935 resinhas proven to exhibit high STL performance, and the double sheetconfiguration having 6 mm air gap proved to offer superior STLperformance.

[0074] Co-injection molding is a process that creates a skin and corematerial arrangement in a molded part. The skin material is injectedfirst into the mold cavity, and is immediately followed by a corematerial. As the skin material flows into the cavity, the material nextto the cavity walls freezes and material flows down a center channel.When the core material enters it displaces the skin material in thecenter of the channel by pushing the skin ahead. As it flows ahead ofthe core material, the skin material continues to freeze on the wallsproducing the skin layer.

[0075]FIG. 1 shows a perspective view of a typical air intake manifold10. Air intake manifold 10 comprises a plurality of shells welded intoone assembly; air intake manifold 10 is constructed of multiple runners12 and plenum 14. Air enters plenum 14 through the throttle body neck16, to be distributed into runners 12, which feed the air into theengine cylinders (not shown).

[0076]FIG. 2 shows a cross sectional view of a co-injection moldedmulti-layer air intake manifold shell 20. Air intake manifold shell 20comprises outer layer 22; sound absorbing core 24; and inner layer 26.Preferably, inner layer 26 and/or outer layer 24 comprises a polyamideresin comprising a nylon resin, a high specific gravity filler,optionally a reinforcement fiber and optionally an elastomer. Thepolyamide preferably comprises at least one of nylon 6, nylon 6/6 andnylon 6/66. The high specific gravity filler preferably comprises amineral and/or a metal filler, more preferably at least one of bariumsulfate and tungsten. The elastomer, if present, preferably comprises atleast one of functionalized ethylene-propylene copolymer, functionalizedstyrene-ethylene butadiene-styrene copolymer and metal salt neutralizedethylene methylacrylic acid di- and ter-polymers. The reinforcementfiber, if present, preferably comprises at least one of glass fibers,carbon fibers and steel fibers. Preferably, the polyamide is present inan amount of from about 20 to about 45 wt. % and the high specificgravity filler ranges from about 40 to about 70 wt. %. The reinforcementfiber may be present in amounts up to about 30 wt. % and the elastomerranges up to about 10 wt. %. One polyamide resin found especially wellsuited for use as inner layer 26 and/or outer layer 24 is Capron® XA2935resin containing glass fibers and mineral filler. Preferably, themineral filler has a specific gravity in the range of 4-20, such asbarium sulfate or tungsten. In the Capron® XA2935 resin, barium sulfateis present in an amount substantially equal to about 53% by weight, andthe amount of the glass fiber reinforcement is substantially equal toabout 15% by weight. Core 24 is alternatively comprised of a low-densitymaterial, such as a polyamide resin, having a foam structure. The foamstructure can be either open- or closed-cell in nature, and produced byeither chemical or physical blowing agent(s), known in the art,introduced into the polyamide resin either in the pellet or melt state.The foam cell structure would have an average diameter range of from theorder of one micron (i.e. via MuCell process) to as large as onecentimeter. The range in reduction of density of the polyamide resin asa result of the foaming process would be 10 to 70%.

[0077] Preferably, core 24 is comprised of a high damping elastomer,such as specific types of thermoplastic elastomers and thermoplasticpolyurethanes available commercially, which are capable of beingco-injection molded with the polyamide resin. One high damping elastomerfound to be especially well suited for use as core layer is apolyamide-based Santoprene, used alone or in-combination with highdamping ‘carbon nanotubes’.

[0078] Optionally the section of the air intake manifold shell, showngenerally at 30 in FIG. 3, is provided with a plurality of blisters 38to distribute localized increased core thickness at predeterminedlocations over air intake manifold shell 30. Such an arrangement ofblisters 38 on air intake manifold shell 30 increases the mass effect.The locations are selected to increase noise transmission losses. Noiseis reduced by shifting the local natural frequencies away from the inputdriving frequency domain and lowering the frequency by adding lumpedmass. The location and the number of the distributed masses or blisterscan be optimized based on the locus and amplitude of noise appointed tobe filtered out.

[0079] In FIG. 4 there is shown another embodiment of the invention. Across-section of an air intake manifold shell is shown in the figure.Double layer air intake manifold shell, shown generally at 40, comprisesinner layer 46 and outer layer 42 of polyamide resin separated by aircore 44. Preferably the air gap has a thickness ranging from about 1about 25 mm, and the polyamide resin layers contain glass fiberreinforcement and mineral filler. The mineral filler is preferablybarium sulfate, present in an amount of about from 40 to about 70% byweight of the polyamide resin composition. The amount of the glass fiberreinforcement present ranges from about 0 to about 30% by weight of thecomposition.

[0080] In yet another embodiment of the invention, the air intakemanifold shell comprises a single layer of Capron® XA2935 resin toachieve superior noise abatement. Optionally, the air intake manifoldshell thickness is not uniform. Air intake manifold shell portionshaving increased thickness are positioned over predetermined areas toincrease noise transmission losses by increasing the mass effect. Eachof the locations is selected to maximize noise attenuation over largeramplitude transmission points, thereby providing increased noisetransmission losses over substantially the entire surface area of theair intake manifold shell. This arrangement of the thicker air intakemanifold shell portions reduces noise by shifting the local naturalfrequencies away from the input driving frequency domain and loweringthe frequency by adding lumped mass. Tailoring the location and thenumber of the distributed masses permits optimum noise attenuation for agiven air intake manifold weight, size and thickness. The air intakemanifold can be constructed economically using a minimum of material,and is small, light, efficient, and highly reliable in operation.

[0081] Having thus described the invention in rather full detail, itwill be understood that such detail need not be strictly adhered to, butthat additional changes and modifications may suggest themselves to oneskilled in the art, all falling within the scope of the invention asdefined by the subjoined claims.

We claim:
 1. A multi-layer engine air intake manifold shell, comprising:a. an outer layer for providing structural rigidity to said air intakemanifold shell; b. a sound absorbing core for dissipating sound energy;and c. an inner layer for providing structural rigidity and heatresistance to said air intake manifold shell.
 2. An air intake manifoldshell as recited by claim 1, wherein at least one of said inner and saidouter layers comprises a polyamide resin.
 3. An air intake manifoldshell as recited by claim 2, wherein said polyamide resin comprises ahigh specific gravity filler and, optionally, glass fibers forreinforcement.
 4. An air intake manifold shell as recited by claim 3,wherein said filler has comprises a mineral and/or a metal filler.
 5. Anair intake manifold shell as recited in claim 4, wherein said fillercomprises at least one of barium sulfate and tungsten.
 6. An air intakemanifold shell as recited by claim 5, wherein the amount of said highspecific gravity filler comprises from about 40 to about 70% by weightof said polyamide resin.
 7. An air intake manifold shell as recited byclaim 3, wherein said reinforcement comprise glass fiber present in anamount ranging up to about 30% by weight of said polyamide resin.
 8. Anair intake manifold shell as recited in claim 3, wherein said polyamideresin further comprise an elastomer.
 9. An air intake manifold shell asrecited in claim 8, wherein said elastomer comprises at least one of oneof functionalized ethylene-propylene copolymer, functionalizedstyrene-ethylene butadiene-styrene copolymer and metal salt neutralizedethylene methylacrylic acid di- and ter-polymers.
 10. An air intakemanifold shell as recited in claim 9, wherein said elastomer is presentin an amount up to about 10 wt. % of said polyamide resin.
 11. An airintake manifold shell as recited in claim 2, wherein at least one ofsaid inner and said outer layers is formed from composition comprising apolyamide resin comprised of at least one of nylon 6, nylon 6/6 andnylon 6/66; a high specific gravity filler comprising at least one ofbarium sulfate and tungsten; glass fiber reinforcement; and an elastomercomprising at least one of functionalized ethylene-propylene copolymer,functionalized styrene-ethylene butadiene-styrene copolymer and metalsalt neutralized ethylene methylacrylic acid di- and ter-polymers. 12.An air intake manifold shell as recited by claim 1, wherein said core iscomprised of a high specific gravity material.
 13. An air intakemanifold shell as recited by claim 1, wherein said core is comprised ofa foam structure.
 14. An air intake manifold shell as recited by claim12, wherein said foam structure is comprised of a foamed polyamideresin.
 15. An air intake manifold shell as recited by claim 1, whereinsaid core is comprised of a high damping elastomer.
 16. An air intakemanifold shell as recited by claim 1, wherein said layers are providedwith a plurality of pockets that permit distribution of localized lumpedmasses at predetermined locations over said air intake manifold shell,said locations being selected to increase noise transmission losses, andto shift resonance frequencies away from preselected regions ofundesirable frequencies identified as rumbling, hissing and air rushnoises.
 17. A double layer air intake manifold shell comprising an innerand outer layer of polyamide resin separated by an air core.
 18. Asingle layer air intake manifold shell comprised of polyamide resincontaining reinforcement fiber and a high specific gravity filler. 19.An air intake manifold shell as recited by claim 18, wherein said highspecific gravity filler comprises barium sulfate.
 20. An air intakemanifold shell as recited by claim 19, wherein the amount of said bariumsulfate filler ranges from about 40 to about 70% by weight of saidpolyamide resin.
 21. An air intake manifold shell as recited by claim18, wherein the amount of said reinforcement fiber ranges up to about30% by weight of said polyamide resin.
 22. An air intake manifold shellas recited by claim 18, wherein the thickness of said layer ranges fromabout 1 to about 25 mm, said thickness being greater over predeterminedareas associated with noise having higher amplitude, to increase noisetransmission losses.
 23. An air intake manifold shell as recited byclaim 18, wherein said shell is formed from a composition comprising apolyamide resin comprised of at least one of nylon 6, nylon 6/6 andnylon 6/66; a high specific gravity filler comprising at least one ofbarium sulfate and tungsten; glass fiber reinforcement; and an elastomercomprising at least one of functionalized ethylene-propylene copolymer,functionalized styrene-ethylene butadiene-styrene copolymer and metalsalt neutralized ethylene methylacrylic acid di- and ter-polymers. 24.An air intake manifold shell as recited by claim 23, wherein said layerhas a non-uniform thickness ranging from about 1 about 25 mm, saidthickness being larger over predetermined areas to maximize noisetransmission losses for a given nominal air intake manifold shellthickness.
 25. An air intake manifold shell as recited by claim 24,wherein said layers are provided with a plurality of pockets that permitdistribution of localized lumped masses at predetermined locations oversaid air intake manifold shell, said locations being selected toincrease noise transmission losses, and to shift resonance frequenciesaway from preselected regions of undesirable frequencies identified asrumbling, hissing and air rush noises.